Brain tumors are the most common solid malignancy of childhood. Primitive neuroectodermal tumors are the most common of these. Using best available therapy, 5 year survival for children with PNET is 60%. Surviving children often suffer cognitive deficits from the effects of antitumor therapy. A better understanding of the genetic alterations and pathways involved in the development of PNET may lead to new types of therapy that prevent recurrence and avoid cognitive deficits in those that survive. Dr. Raffel proposes to study one of these pathways, the sonic hedgehog/PTCH pathway which consists of a number of interacting elements important in the development of the central nervous system. Mutation of the PTCH gene has been shown to cause the nevoid basal cell carcinoma syndrome, one of the few inherited syndromes with which PNET are associated, suggesting that PTCH may function as a tumor suppressor in PNET. Other alterations in the pathway that are functionally equivalent to PTCH inactivation may also play a role in the development of PNET. Besides PTCH, other pathway genes, including hMAD-1, EN2, and PKA may act as tumor suppressors. Overexpression of other pathway genes may also be involved in the development of PNET. The hypothesis of this grant suggests that alterations in the sonic hedgehog/PTCH pathway are involved in the oncogenesis of PNET. To test this, he plans to examine pathway genes and their expression in PNET, based on preliminary data demonstrating LOH at the PTCH locus in 5 of 24 sporadic PNET, with a mutation in the remaining allele in three of the five. In addition, 2 of 12 PNET were shown to have LOH at the EN2 locus. No tumor had LOH at both loci. Alterations in the candidate tumor suppressors of the pathway will be investigated. Expression of pathway genes in the developing cerebellum, the most common location of PNET, will be defined and compared to that of PNET lines and tumors. Effects on tumor cell phenotype associated with transfection of PTCH will be examined in PNET cell lines. These studies will define the role of the sonic hedgehog/PTCH pathway in the genesis of PNET.